Dr. Andres Punning, University of Tartu
Prof. Alvo Aabloo, University of Tartu
Dr. Volker Presser, INM Leibniz Institute for New Materials & Saarland University, Germany
The modern electronics and robotics industry is interested in development of miniature, autonomous, and fully soft devices; consequently, the research on compatible materials is promoted. This work considers one class of materials - ionic electroactive polymer laminate (IEAP), perspective for the given field. An IEAP consists of carbonaceous electrodes with high specific surface area, a porous polymeric separator, and ionic liquid, which fills the pores in electrode and separator. IEAP is a multifunctional material - it is known for its energy storage and actuation capability.
The work at hand explores a novel property of IEAP - generation of electric charge. First, an IEAP laminate was employed in a configuration that corresponds to its use as an electromechanical actuator, but it was bent using an external force. The IEAP generated electric charge proportional to the bending magnitude. Consequently, the same IEAP could be used intermittently as a soft actuator and as a motion sensor.
IEAP consists of highly hygroscopic materials, which is expressed in its high sensitivity to ambient humidity. Electrochemical impedance spectroscopy revealed that reversible absorption of ambient humidity changes the electrical properties of IEAP over one order of magnitude.
In this work, humidity-sensitive IEAP is employed in a novel, unexpected configuration - as a hygroelectrical cell. If an IEAP is placed between environments with unequal relative humidities, electric charge is formed between the IEAP's electrodes. An IEAP can be used to harvest electric energy from the ambient humidity, whereas the magnitude of the generated charge is more than one order of magnitude higher than in the case of the same material as a motion sensor. At this point, the energy storage properties of IEAP are essential - an IEAP hygroelectrical cell does not require additional energy storage units; instead, the generated electric charge is stored in the same part of the material, where it was generated.